Angle in the plane through the beam axis over which
the luminous intensity drops to a stated percentage
(e.g. 50%) of its peak intensity.
Attribute of visual sensation according to which an area
appears to emit more or less light. Brightness according
to the definition is also an attribute of color.
General expression for the color impression received
when looking at a light source.
The facility to change the color temperature of a lighting
installation makes it possible to create a more comfortable
working environment or to introduce dynamic lighting
Ability of a light source to render colors naturally,
without distorting the hues seen under a full spectrum
radiator (like daylight or incandescent lamps). The color
rendering index (CRI) ranges from 0 to 100.
Color rendering index CRI
See Color rendering.
Temperature in kelvin of a full spectrum radiator closest
to the color appearance of a light source at the same
Unit: kelvin, K
Contrast C (between two parts of a visual field)
The relevant luminance difference between two parts
in accordance with the formula:
C=L1 – L2
Where the size of the two parts differs greatly and
L1 = luminance of the smallest part (object)
L2 = luminance of the largest part (background).
The quantity of light that a light source emits per unit
of electrical energy consumed. Notice that the luminous
efficacy can be specified for a light source or for a lighting
system (lamp and ballast). The luminous efficacy of a
system is lower than that of the light source.